Change flow control window size

[RightSeven]

Hi, I want to do some research on flow control like dynamical change window size.

Is there any API can use?
Should I just change the value of QUIC_DEFAULT_STREAM_FC_WINDOW_SIZE and QUIC_DEFAULT_CONN_FLOW_CONTROL_WINDOW?

Please tell me how to do.

[nibanks]

QUIC_DEFAULT_STREAM_FC_WINDOW_SIZE allows you to change the initial flow control window size for streams, but MsQuic owns the logic to dynamically grow that based on app receive speed (see here). QUIC_DEFAULT_CONN_FLOW_CONTROL_WINDOW is used as a fixed window for the connection flow control.

[bizzbyster]

A follow on transport question @nibanks. Is it possible to enable a non-default Congestion Control Algorithm (CCA) like Hybla or BBR? Thanks!

[nibanks]

It's possible to add additional CC algorithms, yes. But they have to be built-in to MsQuic. For instance, see this (draft) PR to add BBR support: #2071.

[bizzbyster]

Interesting - ok I will check this out. As you probably guessed, we would want to enable something like BBR or Hybla (optimized for high latency) to a VpnHood deployment once it has QUIC between client and server as per our discussion here vpnhood/VpnHood#94.

[nibanks]

Yeah, makes sense. Cubic still does a really good job (our current default), so I think it should be more than good enough to start with.